In electronic as well as non-electronic devices, enclosures are commonly used to house device components. These enclosures perform several functions including providing structural support to the device components and vibration dampening. The enclosures are also referred to as housings. One example of an enclosure for an electronic device is a computer chassis. Typically, a computer includes a chassis that is generally a metallic frame. The chassis typically houses circuit boards, power supplies and wiring. The chassis typically includes four sidewalls and top and bottom elements. Generally, at least one of the chassis includes a removable cover such that the chassis components are easily accessible for replacement and repair purposes. The walls are typically thick and rugged such that they provide a robust structural support for the enclosed components.
The walls often enclose device components that can malfunction and cause device failure when they overheat. Some device components dissipate heat during their operation. They are referred to as heat sources. An example of the heat source includes the integrated chips that comprise the circuit boards installed in the computer chassis. The heat generated by the heat sources can damage not only the heat sources themselves but also the other components enclosed by the walls. To avoid device failure, therefore, the heat in the interior of the enclosure must be effectively managed. A common heat management technique includes designing a well-ventilated enclosure such that the heat can dissipate to the exterior of the enclosure. Another technique includes fabricating the enclosure from materials with high thermal conductivity. Still another technique includes installing a cooling fan inside the enclosure. Yet another effective heat management technique includes using a thermal transport device to absorb the heat from the interior of the enclosure and transfer it to a heat sink. The heat sink can include a cooler portion of the chassis away from the heat source. A well-known thermo-siphon device is the heat pipe, the configuration of which can be custom designed for the space and application.
While many of the structures and chassis provide proper structural support, there is a need to have lighter structures. Composite structures, such as electronics enclosures, have the potential to provide significant weight savings for a variety of systems. For vehicles, weight savings are directly tied to power consumption. Reducing vehicle power consumption provides advantages such as increasing range, improving fuel efficiency, and allowing for the use of more complex and power hungry systems. While composite structures can provide these savings, they exhibit poor thermal conductivity. This has limited their application to components with little to no heat flux or power.
Carbon fiber reinforced polymer (CFRP) composite material is a highly attractive structural material in applications where mass is critical. The carbon fiber matrix provides strength comparable to steel in a material with only about 25% of the density. In many instances, the carbon fiber reinforced polymer sheet can also be made thinner than a metal sheet would have to be made, further increasing the mass savings. Almost any portable equipment can benefit from less mass, which translates into less energy required to move the object. Thus, many automobiles and other transportation equipment employ carbon fiber reinforced polymer laminates for some components. In airplanes, weight becomes even more critical, since every ounce must be countered by lift forces in order to stay aloft, thus carbon composite materials are common on many state-of-the-art aircraft.
Thermal challenges have arisen with the increased use of composite structures in applications where excess heat is being generated within the structure. Where traditional metal structures can be designed to conduct and spread heat out over large external surfaces, composites have poor thermal conductivity and cannot be used in this manner. In effect, a composite enclosure acts to insulate the internal components. As a result, heat generated by components is trapped and the inside becomes hotter and hotter, which is detrimental to the performance and reliability of the electronics housed by the enclosure. For comparison, carbon fiber reinforced polymer materials typically have thermal conductivities on the order of 5 W/m-K, while carbon steel is near 50 W/m-K and aluminum is near 200 W/m-K. Therefore, the use of carbon fiber reinforced polymer composites for electronic enclosures is currently limited to applications where the heat dissipation requirement is low.
It would, therefore, be beneficial to provide a light weight structure which provides an alternate thermal path through the material to reduce the thermal penalty associated with the use of these materials without negating the benefits provided by their low mass. It would also be beneficial to provide an effective closure design which properly dissipates heat without the need to customize the structure and the heat paths for each application.